Ink-jet pens comprise a reservoir of ink and a printhead comprising a plurality of orifices from which ink is expelled toward a print medium, such as paper. Between the reservoir of ink and the printhead are passages, including a plurality of firing chambers and a plenum for supplying ink to the firing chambers. Each firing chamber includes a resistive heating element, which is energized upon demand to fire a droplet, or bubble, of ink through the orifice associated with that resistor.
The orifices through which the ink is expelled in the printhead are on the order of 50 .mu.m in diameter. The passages can be as small as widths of .about.40 .mu.m and heights of .about.25 .mu.m. Any particles larger than about 25 .mu.m can become trapped at various locations within the pen in or near the firing chamber and cause clogging. Of course, smaller particles can also become trapped, depending on the aspect ratio of the particle. Such clogging, of course, interferes with the quality of the printed image.
Present ink-jet pens have a fine mesh filter to separate internal particle contamination from the bulk ink supply before the ink reaches the firing chambers. The mesh is sized to about 25 .mu.m. However, as ink-jet technology is used to produce higher resolution printing, a smaller diameter jet, or orifice, is required. This is achieved by decreasing printhead nozzle diameter. As a result, an increase in the internal particle problem is anticipated. If this is true, then a finer mesh filter may be required, which in turn would require a larger filter area so as to minimize pressure drop across the filter. These changes would affect pen design, cost, and manufacturing strategy.
A solution to the problem of particle contamination is addressed by European Patent Application No. 92102748.8. A plurality of lands are provided, both near each entrance to a firing resistor and between the entrances.
However, a further problem exists in the construction of pens employing a ink feed channel acting as a common reservoir of ink. Namely, a nozzle plate, which contains the nozzles through which the ink is expelled, tends to sag in unsupported areas, including over the ink feed channel. Such pens are referred to as "top-shooter" or "roof-shooter" pens. The sagging nozzle plate can pinch off the supply of ink, thereby reducing the usefulness of the pen.
The above-mentioned European Patent Application is directed to the so-called "side-shooter" thermal ink-jet configuration, and this configuration does not have a common ink refill channel through the substrate on which the firing resistors are formed, but rather has a plurality of orifi through the top of a cover plate for introducing ink into a common area. There appears to be no problem with sag of the cover plate associated with the side-shooter configuration.
Accordingly, there remains a need to support the nozzle plate in the vicinity of the ink feed channel and to remove particle contamination from the ink in ink-jet pens.